Polyvinyl acetate and acrylic-based emulsions are used extensively in adhesives in many applications, including furniture construction, vinyl laminating, pressure sensitive adhesives, consumer glues and food packaging. One major area of interest is film laminates. Such multilayer film constructions are used to package foods and consumer products and offer a combination of properties not obtainable with a single product. Often paper is used for mechanical strength and is bonded to a plastic film to give a packaging material which has improved water resistance.
Joining dissimilar films can be accomplished in several ways; one is by coextrusion of two or more thermoplastic materials. Laminating films as they exit the extruder gives a multilayer film which has good mechanical integrity, as long as the materials are not too dissimilar chemically. Films which have markedly different surface energies may not have sufficient adhesion to hold together. Often adhesive tie layers are used to improve layer to layer adhesion.
An alternate method of construction is the use of adhesives to laminate films together. Aqueous vinyl acetate-based and acrylic-based polymer emulsions are commonly used to bond porous substrates, such as paper, to plastic films including polyvinyl chloride, polyethylene terephthalate, polyethylene, polypropylene and the like. Such emulsions have the required properties of wet tack, adhesive strength and runnability to be used in high speed laminating lines.
Often the adhesive strength between the two films of interest is insufficient for the required end use. In such cases, it is common to use an adhesion promoter to improve the adhesive strength. One compound in current use as an adhesion promoter is polyethylenimine (PEI). Addition of PEI at 0.5 to 2% of the polymer weight in the emulsion commonly gives improved adhesion on low surface energy films. Such adhesion is commonly measured by the T-peel test.
Representative of art teaching the use of polyalkylenimine resins such as PEI resins in film laminates include the following:
U.S. Pat. Nos. 2,828,237; 3,033,707; 3,096,602; 3,140,196; 3,230,135 and 3,361,586.
JP4-264182 discloses a wood adhesive composition comprising a polyvinyl alcohol A, a filler B and a waterproofing agent C; each molecule of the polyvinyl alcohol containing at least one type of functional group selected from among primary amino groups, primary ammonium salt groups, secondary amino groups, and secondary amino salt groups. The adhesive composition may also contain an aqueous polymer emulsion D at 5 to 400 weight parts per 100 weight parts of polyvinyl alcohol A.
U.S. Pat. No. 5,326,809 discloses a method for preparing aqueous emulsions in the presence of a poly[(vinyl alcohol)-co-(vinylamine)] copolymer [PVOH/PVAm] as a protective colloid and aqueous polymer emulsions containing such copolymer. Polyvinyl acetate emulsions prepared using such copolymer as a stabilizing agent were tested as single lap shear adhesive joints employing maple wood adherends.